西峰油田微观孔隙结构对注水开发效果的影响

The influences of microscopic pore structure on waterflooding effectiveness in Xifeng Oilfield

目的探讨西峰油田长6、长8储层微观孔隙结构对注水开发效果的影响。方法综合运用常规微观孔隙结构研究方法和真实砂岩微观模型水驱油、CT扫描、核磁共振等技术。结果西峰油田合水区、庄19区块长8储层和庄40区块长6储层的孔隙连通情况、孔喉比大小影响着渗流规律和注水开发效果;实验发现,微裂缝的存在使得水驱油机理和效果均发生了改变,只要有微裂缝存在,即使整体渗透率很小,在较低的压力下,注入水就可以进入前行,但水驱效果差;贾敏效应的存在增加了水驱油压力,且渗透率越低,水驱油与油驱水压力差越大;压敏效应对特低渗透储层(尤其是微裂缝储层)的注水效果影响明显。结论孔隙结构差异性、微裂缝、贾敏效应和压敏效应是影响注水开发效果的根本原因。

Aim To make definite the influences of microscopic pore structure of Chang 6, Chang 8 reservoir on waterflooding effectiveness in Xifeng oilfield. Methods Conventional research methods of microscopic pore structure, water displacing oil experiments of actual sandstone microscopic model, CT scanning and NMR technique are applied synthetically. Results Flow law and waterflooding effectiveness are affected by the pore communication and pore throat ratio in Chang8 reservoir of Heshui and Zhuang19 area as well as in Chang6 reservoir of Zhuang40 area in Xifeng oilfield. It is learned from experiments that microcracks alter water/oil displacement mechanism and water/oil displacement effectiveness. Even if the permeability of reservoir is low, injected water can go forward in lower pressure as long as the microcrack presents. However, the waterflooding effectiveness is bad. Jamin action increases the water/oil displacement pressure. Moreover, the differential pressures between water displacing oil and oil displacing water will become greater with the lower permeability. The pressure-sensitive action effects waterflooding effectiveness apparently for extra-low permeability reservoir, especially for microcrack reservoir. Conclusion Difference of pore structure, Jamin action microcrack, and pressure-sensitive action are the essential reasons to influence waterflooding effectiveness.